Exemplary embodiments of the present invention relate generally to a system and method for identifying impaired electrical equipment. More particularly, some exemplary embodiments of the present invention relate to a system and method for detecting impaired electric power equipment. Exemplary embodiments of the present invention may also be useful for testing various other types of electrical systems. Furthermore, exemplary embodiments of the present invention may be useful for stationary and/or mobile testing of various types of electrical systems.
Power generation, distribution, transmission, and substation systems are just some examples of electrical systems. Some other examples of electrical systems include radio systems, communication systems, control systems, industrial electrical systems, and other types of electrical circuitry and systems. In addition, many other types of electrical systems are known or may be developed.
Any type of electrical system may be responsible for creating electromagnetic radiation. Electromagnetic radiation includes radio frequency radiation as well as other frequencies of electromagnetic radiation. The underlying cause of the electromagnetic radiation may limit or disrupt the operation of the electrical system that is emitting the electromagnetic radiation. Moreover, electromagnetic radiation may also interfere with the operation of other electrical systems. In fact, many sophisticated electrical systems are becoming increasingly sensitive to the effects of electromagnetic radiation. Consequently, electromagnetic radiation may sometimes be referred to as electromagnetic interference (EMI). A common definition of EMI is “any electromagnetic disturbance that interrupts, obstructs, or otherwise degrades or limits the effective performance of electronics/electrical equipment.”
The causes of electromagnetic radiation vary. Equipment such as electrical appliances, electronic equipment, motors, circuits, and other electrical systems can produce electromagnetic radiation, which can be influenced by the surrounding environment such as hills, trees, buildings, and other environmental factors. In addition, impaired electrical equipment may be the cause of an increased level of electromagnetic radiation. Other causes are also possible. Regardless of whether the cause of electromagnetic radiation is intentional or inadvertent, hostile or friendly, or caused by jamming devices, malfunctioning equipment, or improper system operation, the resulting electromagnetic radiation can have detrimental impact on the operation of electronics and other electrical systems.
A standard for defining power disturbances has been established by the Institute of Electrical and Electronics Engineers (IEEE) in order to help address the problems caused by electromagnetic interference. In particular, the “IEEE Recommended Practice for Monitoring Electrical Power Quality” defines electrical disturbances as interruptions, sags and swells, long duration variations, impulse transients, oscillatory transients, harmonic distortion, voltage fluctuations, and noise. In addition, the standard sets forth acceptable disturbance levels, and electrical equipment manufacturers use EMI (e.g., radio frequency interference) shielding techniques in attempts to meet the standard.
There has been growth in the level of EMI shielding that is required as well as in the number of new applications that require shielding. However, the development of new shielding technologies has not kept pace with the development of new electrical systems. In addition, enhancements to old shielding technologies have also lagged behind the development of new electrical systems. In fact, shielding of electrical systems from the effects of electromagnetic radiation is commonly viewed by manufacturers as adding little or no value to the electrical systems. Thus, the development of shielding has been relatively stagnant in recent history.
Compounding this problem is the fact that EMI detection techniques have not advanced rapidly enough in light of the development of new types of electrical systems. There are currently few research and development activities to develop new devices to identify the causes of EMI. As a result there are little to no quality commercial EMI diction devices available. Currently commercial EMI detectors suffer from poor construction and lack the tolerances necessary to reliably detect and locate EMI. Most commercial EMI detectors have a wide passband but still employ a shallow rolloff. Commercial EMI detectors only work with a particular frequency and lack the variety necessary to be effective. Another problem with most commercial EMI detectors is that they are susceptible to standing waves. This susceptibility to standing waves interferes with the EMI detectors ability to locate the disturbance. As a result, EMI is an increasing problem.
Power line arcing is one example of a cause of EMI. As a result of the high voltage, power line arcing may be destructive, and it may indicate that certain electrical equipment is in an impaired condition. In fact, any type of arcing may indicate that electrical equipment is in an impaired condition.
Arcing occurs when a sufficiently large potential difference develops between two objects. For example, a small gap between components of energized electrical equipment may lead to arcing, wherein an electrical charge builds up and discharges across the gap. The cause of a gap may simply be due to expansion and contraction or corrosion of the equipment. As a result, small gaps in the electrical equipment can be very difficult to identify. Compounding the difficulty is the fact that some electrical equipment such as power lines may be located well above ground level and energized with high voltage, making it impractical or inefficient for electrical utility personnel to visually inspect each structure or other elevated equipment in an attempt to locate an impaired piece of electrical equipment. Impaired equipment can still be difficult to locate even if the equipment is located near ground level. For instance, multiple pieces of electrical equipment in a general area such as a room, a factory building, or even a general outside area can hinder the detection of an impaired piece of equipment. As a result, the location of impaired electrical equipment may be difficult to identify.
In light of the difficulty in locating impaired electrical equipment, there is a need for a system and method for detecting impaired electrical equipment that may utilize the characteristics of the arcing. The pulse repetition rate is the rate at which arcing occurs across a gap, which may be measured by the number of arcs per unit time. The pulse repetition rate is typically proportional to the source voltage and inversely proportional to the width of the gap. Consequently, with everything else being equal, a higher voltage results in a higher pulse repetition rate, and a wider gap results in a lower pulse repetition rate. In addition to the pulse repetition rate, arcing has an RF frequency characteristic. In particular, arcing results in the production of a radio frequency signal. In the case of EMI, the signal is typically broad spectrum such that it is detectable across a wide band of the radio frequency spectrum. Each arc produces a radio frequency signal; therefore, as the width of the gap or the source voltage changes, the resulting radio frequency signal also changes. Other factors may also affect the RF frequency. For example, with regard to a utility pole, the RF frequency may also be affected by: the height of the utility pole; whether or not a ground wire runs along a side of the utility pole; the distance between the utility pole and adjacent poles; the components (e.g., insulators, cutouts, etc.) that are mounted at the top of the utility pole; and whether the utility pole is a single-phase or three-phase structure. Other factors may also impact the RF frequency. All of these parameters can and often do act as ‘antenna tuning elements’ that affect the signal that is radiated when an arc occurs. As a result, during any given 60 Hz cycle, for example, there may be a family of different RF signals produced. Finally, arcing may have a modulation frequency. The modulation frequency of the arcing is not dependent on the level of the source voltage or the width of a gap between electrical components. In this sense, the modulation frequency is an independent characteristic of the radio frequency signal(s) produced by arcing. In other words, with regard to arcing caused by an alternating current (AC) source, the modulation frequency is a characteristic of the frequency of the source.
Exemplary embodiments of the present invention are directed to a system and method for detecting impaired electrical equipment. An exemplary embodiment of the present invention may receive electromagnetic radiation and process the resulting signal. For example, signal processing in some embodiments of the present invention may be used to identify electromagnetic radiation having a particular characteristic. Exemplary embodiments may utilize a wide and flat passband filter to combat and eliminate the problem of standing waves. The use of a wide filter with a flat passband causes a cancellation effect among various frequencies within the passband when the EMI detector is not at the exact source. This results in a EMI detector that may be immune to the false source phenomenon that other EMI detectors experience. This allows exemplary embodiments to locate the disruption more efficiently. To aid with location of disruption, exemplary embodiments take readings at multiple frequencies and use an averaging technique to guide a user to the location. This averaging function may occur inherently as a function of the wide filter employed. Furthermore, an exemplary embodiment of the present invention may also include the determination of the time and/or location during testing. As a result, an exemplary embodiment of the present invention may be useful for stationary and/or mobile testing of an electrical system.
In addition to the novel features and advantages mentioned above, other features and advantages of the present invention will be readily apparent from the following descriptions of the drawings and exemplary embodiments.